I am looking at a job to wire a large home with an attached 800 sq. Ft. mother in law suite. I will be running a 125A sub panel which will feed this area. I am looking at installing some sort of CT so that the homeowner will be able to keep up with the electric usage of the mother in law suite. Have any of you guys ran into this type of installation and if so is there a particular product you would recommend. Thanks in advance.
Sub metering
- Thread starter mccayry
- Start date
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texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
I second that. I used to say "where you going to get a isolated neutral meter socket", but I learned here that Milbank actually makes one now. Or you could go the EMon route.
fmtjfw
Senior Member
- Location
- Fairmont, WV, USA
Or just don't bond the neutral to the second meter socket. Neutral is not needed for normal 120/240 3 wire service. The socket should be connected to the EGC though. Even if it were a 5 or 7 jaw meter you could lift the Neutral connection from the grounding bar and feed it from the neutral.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Make sure you check local laws. Sub metering to a tenant space is tightly controlled in many places and completely banned in some.
readydave8
re member
- Location
- Clarkesville, Georgia
- Occupation
- electrician
I'm not sure if the sub-metering is an issue, but rather the billing resulting from the sub-metering?
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Yes, billing is the issue.
Some places require that the tenant be billed directly from POCO, putting a private meter inline with a apt feeder that comes from the house panel is not always allowed.
Also many places require the tenant to have access to the meter so he/she can read it also.
My answers are based on the assumption that the apt. is a rental.
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I will check with AHJ and POCO to make sure this would be ok.
fmtjfw
Senior Member
- Location
- Fairmont, WV, USA
Sub metering and revenue. In WV it is forbidden for any entity other than a power company to sell electricity. Many years ago I recovered an apartment deposit the landlord was holding for "excessive power usage" using that law and a gentle reminder from an attorney.
I've used sub metering for my amusement, putting two A-base meters on the feed from PV panels to record the on- and off-peak power production.
If I had a home office I might put in a sub meter for it, not for revenue, but for tax deduction.
You can get KWH meters pretty cheap off EBAY. If you get an electronic one it will probably not be zeroed and you probably will not be able to zero it (without a friendly meter technician). If you get a mechanical one you can pop the glass and reset it (just like an odometer) or disassemble the gear train and zero it quicker.
My father was a metering engineer basically his whole adult life. We used to use Murray Seals as key rings (I still have a few laying around). If I cut a Murray Seal as part of a service change, I just tell then, don't want to stick in a metal one and really confuse them.
I've used sub metering for my amusement, putting two A-base meters on the feed from PV panels to record the on- and off-peak power production.
If I had a home office I might put in a sub meter for it, not for revenue, but for tax deduction.
You can get KWH meters pretty cheap off EBAY. If you get an electronic one it will probably not be zeroed and you probably will not be able to zero it (without a friendly meter technician). If you get a mechanical one you can pop the glass and reset it (just like an odometer) or disassemble the gear train and zero it quicker.
My father was a metering engineer basically his whole adult life. We used to use Murray Seals as key rings (I still have a few laying around). If I cut a Murray Seal as part of a service change, I just tell then, don't want to stick in a metal one and really confuse them.
K8MHZ
Senior Member
- Occupation
- Electrician
I have seen 'land lord meters' that were simply reading a couple of CTs. The purpose was not to figure monthly bills from (not legal in MI) but to monitor usage as a basis for rent adjustments at agreement time.
How would a meter using CTs be able to tell the difference between watts and kVAs?
How would a meter using CTs be able to tell the difference between watts and kVAs?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
In reality, at their most basic all meters use some type of CT.
Why do you think there might be a problem?
K8MHZ
Senior Member
- Occupation
- Electrician
Don't CTs just measure amps?
I see there are also hand held clamp on watt meters. I guess I am just used to CTs only being used to determine amps and thought they were too 'dumb' to be able to indicate true power.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
120430-1141 EDT
K8MHZ:
From the output of a current transformer, a resistive shunt, a Hall type current sensor, etc. you get an output that is an instantaneous measure of current. Some of these sensors devices will work with DC as well as AC, and others AC only.
If you also have a sensor that has an output of the instantaneous voltage, then you can multiply the instantaneous current and voltage and get instantaneous power. Average the instantaneous power to obtain average power. Integrate average power over time to get the energy over the integration time.
This is what a KWH meter does. It may or may not use current transformers.
I believe you have a Kill-A-Watt. It uses a resistive shunt in the neutral leg and multiplies the shunt voltage with the hot to neutral voltage to obtain power. The Kill-A-Watt works better on low power factor loads, an unloaded single phase motor, than does the TED 1000 that uses current transformers.
If you obtain only the RMS current from a current transformer, as in the use of a clamp on current meter, then you do not have a direct way to measure power.
.
K8MHZ:
From the output of a current transformer, a resistive shunt, a Hall type current sensor, etc. you get an output that is an instantaneous measure of current. Some of these sensors devices will work with DC as well as AC, and others AC only.
If you also have a sensor that has an output of the instantaneous voltage, then you can multiply the instantaneous current and voltage and get instantaneous power. Average the instantaneous power to obtain average power. Integrate average power over time to get the energy over the integration time.
This is what a KWH meter does. It may or may not use current transformers.
I believe you have a Kill-A-Watt. It uses a resistive shunt in the neutral leg and multiplies the shunt voltage with the hot to neutral voltage to obtain power. The Kill-A-Watt works better on low power factor loads, an unloaded single phase motor, than does the TED 1000 that uses current transformers.
If you obtain only the RMS current from a current transformer, as in the use of a clamp on current meter, then you do not have a direct way to measure power.
.
K8MHZ
Senior Member
- Occupation
- Electrician
- Status